1. Field of the Invention
The present invention relates to flexible hoses, a manufacturing method thereof and an extruder, and more particularly to flexible hoses which are suited to be used as suction hoses of electric vacuum cleaners, a manufacturing method thereof and an extruder.
2. Description of Related Art
Conventionally, as a suction hose of an electric vacuum cleaner, a hose is known by Japanese Patent Publication No. 1-21973 wherein a hose body is formed by spirally winding a strip made of synthetic resin and a conductor is contained in a cavity formed in the strip.
However, in the above hose, the cavity to contain the conductor is formed by folding an edge of the strip, and the manufacturing process is complicated. Also, the cavity is not large enough to provide a space for the conductor contained in the cavity to move freely, i.e. when the hose is bent, the conductor can not move in a diametrical direction to the hose and may break under stress. To withstand the stress, the conductor has to reach a specified thickness, and it causes a problem of raise in cost for the hose.
On the other hand, conventional flexible hoses are manufactured in such a way that: a strip of a specified width and thickness made of soft resin in a melted state is extruded from a die of an extruder; and the strip is spirally wound around rotating shafts for forming a hose with the strip overlapping previously wound portion; thus the strip forms a hose body; at the same time, a wire made of hard resin in a melted state is joined to the hose body by fusion as a spiral reinforcement.
What is used as a strip made of soft resin to form the above hose body is a resin tape which is extruded from a die of a straight head of an extruder. On this condition, there is a case that modifying width or thickness of the resin tape is needed according to usage or desired properties of the hose. In such a case, for example, in order to thin the resin tape without changing its width, decreasing the extruding volume of the resin or speeding up in pulling out the resin tape while using the same die was tried. However, the object was not achieved because the width of the resin tape also narrowed.
It means that the shape of the opening for discharging resin of one selected die almost determines the width and the thickness of the resin tape, i.e. it is impossible to form another resin tape of different width or thickness without changing dies. Accordingly, each time to modify the width or the thickness of the resin tape, the operations of: changing dies for the appropriate size; extruding a resin tape; and forming a hose; are necessary. Such operations require equipment of various shapes of dies, and the operation of changing dies is complicated and costs much time. Thus, there is a problem of inefficiency.
Therefore, an object of the present invention is to provide a flexible hose wherein a conductor, which is a component of an electronic circuit of a remote switch or for driving a power brush etc., is relatively free to move.
Another object of the present invention is to provide a flexible hose wherein the conductor will not break even if an inexpensive thin wire is used for the conductor.
Further, another object of the present invention is to provide a flexible hose which does not use polyvinyl chloride resin (PVC), the use of which tends to be restricted under the recent global environmental problems because it is deemed that burning waste PVC generates noxious gas.
Another object of the present invention is to provide a flexible hose and a manufacturing method thereof wherein width and thickness of a strip can be adjusted freely with one die of an extruder without changing to another die.
Further, another object of the present invention is to provide an extruder which is capable of inserting a conductor easily in a reinforcement of hard synthetic resin which is to be spirally wound and joined onto an outer surface of a hose body of soft synthetic resin.
In order to achieve the above objects, a flexible hose according to the present invention comprises a hose body made of soft synthetic resin, a reinforcement made of hard synthetic resin which is spirally wound and joined to the hose body by fusion, and a conductor arranged inside the reinforcement in its longitudinal direction, the conductor being inserted in a space made in the reinforcement when the reinforcement is formed by extrusion molding of the hard synthetic resin so as not to adhere to the reinforcement and so as to be movable.
In the flexible hose according to the present invention, because the conductor is relatively movable, straining or compressive force does not act on the conductor, and the possibility of breakage of the conductor is small. Therefore, a thin conductive wire can be used with no problem, and the cost for the hose can be lowered.
Further, the flexible hose containing the conductor inside uses only soft and hard synthetic resin, does not require any complicated manufacturing apparatus or processes, it is easily manufactured by a general purpose extruder, and further meets the requirement for quitting the use of PVC.
Also, the flexible hose according to the present invention comprises two reinforcing members wound around a hose body in parallel to each other, and the conductor is arranged in each of the reinforcing members. The conductors correspond to an anode and a cathode respectively, and means for distinguishing the polarity of the conductors is provided. The means for distinguishing the polarity is a difference in color, and for example, the means is achieved by plating at least one of the uncovered conductors.
Further, the flexible hose according to the present invention is manufactured by the following processes of: extruding a tube made of soft resin from a head of an extruder; then pressing and flattening the tube to form a strip; and winding the strip spirally with its adjacent side edges joined together to form a hose body. It is preferable that a reinforcement made of hard resin is further wound spirally and joined to the hose body by fusion.
In the manufacturing method according to the present invention, as the strip to form a hose body, a cylindrical tube extruded from a cross head of an extruder is used. The cylindrical tube is pressed and flattened while in a melted state right after the extrusion. This strip formed of the flattened tube is spirally wound, and the adjacent side edges of the spirally wound strip are joined together simultaneously with fusion joining of a spiral reinforcement made of hard resin in a melted state onto the adjacent side edges. In this method, it is possible to adjust the width and the thickness of the strip freely without changing dies in manufacturing the flexible hose.
If an extruder with a cross head die is used, it is possible to blow air into a tube which is being extruded continuously, and thus, an enlargement of the tube in diameter is possible. The enlarged tube will be formed into a wider strip when it is flattened. Thus, it is possible to adjust the width of the strip freely by properly enlarging the tube in diameter. Also, it is possible to adjust the thickness of the strip freely by properly adjusting the thickness or the biased thickness of the tube.
An extruder for extrusion molding hard synthetic resin into a reinforcement, which is to help a hose body made of soft synthetic resin keep its shape, while inserting a conductor in the reinforcement to be movable in the reinforcement, said extruder comprising: a passage through which the hard synthetic resin for the reinforcement is extruded; and a thin tube-like guide through which a conductor is to be inserted longitudinally in the reinforcement extruded from the passage, a tip of the guide slightly sticking out of an exit of the passage or being on a level with the exit of the passage.
In the extruder according to the present invention, since the tip of the guide to guide the conductor in the reinforcement slightly sticks out of an exit of the passage or is substantially on a level with the exit of the passage, it is possible to insert the conductor in the reinforcement longitudinally so that the conductor is movable therein.
At the exit of the passage, a higher pressure is applied to the hard synthetic resin which is being extruded through the passage because the passage becomes narrower around the exit. If the tip of the guide is in the passage, the hard synthetic resin which is being extruded through the passage will flow backward into the tube-like guide, and the hard synthetic resin will adhere to the conductor. Then, in this case, the conductor cannot be inserted in the reinforcement to be movable therein.